Process for effecting anion exchange



. Patented July 16, 1940 Oliver M. Urbain and William R. Stemeri,Columibus, Ohio, assignors Harpster, Ohio to Charles H.

No Drawing. Application April 5, i939, a Serial No. 266,196-

4 Claims.-

-This invention relates to the preparation-and use of materials for therecovery or removal of inorganic anions by anion exchange processes.

More specifically, the invention relates to the- 5 preparation and useof metal salts containing exchangeable hydroxyl anions for the treatmentof liquids from which it ,is desired to recover or remove other anionsby an exchange process.

It has long been known that certain natural 10 materials, as well ascertain synthetic materials, are capable of eifec'ting the exchange ofpositive ions (1. e., cations). These materials, known as zeolites orhydrated alumina-silicates, have found wide use for softening water dueto their faculty of base or cation exchange and their case of ormagnesium cations, with a sodium chloride solution, by which means asodium zeolite is 25 again produced which may be reused to softenadditional quantities of water. Many artificial" zeolites have beenprepared and are now extensively used to eliminate the hardness formingcompounds from municipal and private water supplies. The fundamentalcharacteristic of these zeolites is that they have within theirstructure an ionizable cation, while the rest of the compoundisinsoluble. v

It is the purpose of our invention to provide materials which possessanion or acid exchange properties analogous to the cation .or base ex-,

change properties of the zeolites. It is further an object of ourinvention to provide the methods by which these materials may beprepared. and 40 the processes by which they may be utilized to efiectanion or acid exchange. It isadditionally an object of our invention toprovide methods of regeneration of such materials. In general, it is 45highly novel and extremely practical anion or.

acid exchange process similar-to that above described in the cation orbase exchange field.

We have discovered that certain compounds as o hereinafter describedpossess the unusual prop- M represents a polyvalent metal, and Z" thebroad object of this invention to provide a erty of exchanging negativeions -or anions. These compounds, which we refer to as anion exchangesalts, possess the fundamental characteristics of having within theirstructure an 'ion'izable hydroxyl anion while the rest of the compoundis-insoluble. The basis of our invention lies in the ability of theionizable hydroxyl anion to dissociate from the insoluble portion of"the molecule and exchange its position with that of anotherionizableanion in liquids which are being treated. p

The compounds which We have found will eifect anion exchange are thosewhich contain within their molecules, at least, one --M-A group and aradical composed ofan amphoteric metal atom and at least two oxygenatoms attached thereto, each .MA group being linked by valence to one ofsaid oxygen atoms, and in which group,

represents an ionizable hydroxyl anion, We have found that the metalrepresented by M may be any polyvalent metal, such, for example, ascalcium, magnesium, zinc, mercury, iron, alumi: num, barium, tin, andstrontium. 7

By radicals composed of amphoteric metal atoms and oxygen atoms, we meanthose selected from the class comprised of titanates, phosphates,-

I borates, sulfites, silicates, borosilicates, aluminates, tellurates,selenates, zirconates, antimonates, stannates, stannites,-ferrates,ferrites, arsenates, cerates and other such oxygen-amphoteric metalradicalsl There may be one'or more oxygen-amphoteric metal radicalscontained within the molecules, and they may be the same or differentradicals. vention to materials containing these elements alone forwehavei'ound that all compounds containing the metal-anion groupingsattached to oxygen atoms ofoxyg'en-amphoteric metal radi-- cals effectinvarying of anions.

such compounds is'the MA groupings attached to oxygen atoms ofoxygen-amphoteric metal radicals. In those compounds. the oxygen isattached to the metallic atom of the oxygenamphoteric metal radical, themetal is attached to the oxygen, and the lonizable hydroxyl anion We donot limit our indegrees the exchange 0 As we have pointed out, theactive portion of The oxygen-amphoteric metal radical portion and themetal portion of the materials act as supports and vehicles serving aschemical conditioners to place the hydroxyl anion in a favorableposition for ionization and exchange. The oxygen-amphoteric metalradical portion' also serves the fundamental purposes of providing highsurface exposure and desired insolubility.

Since the ionizable hydroxyl anion is held by true valency forces," theprocess of anion exchange which is effected by the materials describedis a substitution process in which the anions of the liquid to betreated chemically replace the hydroxyl anion of the exchange materialin a manner analogous to base exchange or cation exchange processes nowin common use. It will beobserved that in our materials there is presentthe essential advantage that the anions are held by true valency forcesin contra-distinction to any physicalphenomena of adsorption or likeprocess.

Another property of these materials is their ability to effect selectiveanion exchange. though all anions may be exchanged by these materials,we have found that all anions do not exchange with the same ease. Byvarying, the

conditions of operation, we may produce the desired result in varyingdegrees.

The compounds which we have discovered will effect anion exchange arethose which conform to the following general formula:

, Ra lZdAK h in which R is an oxygen-amphoteric metal radical, M is ametal, "A is an anion or negative grouping, the exponents representvalences, and the subscripts represent the number of atoms or radicalstaken up to form the molecule. In this formula, b equals 2 or more, anda, c, e, and I each equal 1 or more.

It is necessary that the total theoretical basicity of theoxygen-amphoteric metal radical acids making up the active portions ofour material equal:

which makes possible our process of anion exchange.

In our applications Serial No. 38,664; 143,628

. and 143,631, filed August 30, 1935, May 19, 1937 and May 19, 1937respectively, of which this application is a continuation in part, wehave described broadly the class of materials with which we may effectanion exchange. The exchange of anions by our processes is not, however,limited to materials in which the ionizable anion is that of aninorganic acid, as claimed in Patents No. 2,157,510 and No. 2,157,511which issued on those applications on May 1939. Materials in which theionizable anion is a hydroxyl ion may also be effectively employed toexchange anions.

Illustrative of the materials with which we may eflect anion exchange wegive the following structural formulae, which show the relationship ofthe ionizable hydroxyl anions to the 'insoluble portions of thematerials.

0-Ba--0H o=s1 0-H Barium silicate hydroxide O-0uOH -0=Ti\ 0-Cu-0H Cuprictitanate hydroxide OSr-0H 0=P-0Sr-0H O-Br-OH Strontium phosphatehydroxide /0H O-Fe-OH O= Ae-0Fe on 0Fe OH 0H Ferric arscnate hydroxide o/0-Ba0H Be\ 'ii\ 0 0'Ba-OH Barium ortho-titanste hydroxide 0 /0H Sr 81 oo-ce-ou Calcium strontium ortho silicate hydroxide O=Al0- on 0=Al0 onBtannic aluminate hydroxide These are exemplary of the hydroxylcompounds which may be utilized in eif ecting anion exchange. We haveprepared others, such as the zinc, mercury, cobalt, nickel, cadmium,andv manganese salts of the oxygen-amphoteric metal radical classenumerated above in addition to those shown. I

We shall now describe several methods which we have utilized forpreparing anion exchange compounds of this type.

Method A.-An acid of one of the oxygen: amphoteric metal radicalcompounds may be reacted with a hydroxide of a polyvalentmetal.

For example, silicic acid may be mixed with barium hydroxide, and fusedat elevated tempera tures for several hours. The resulting mixture isallowed to cool and is then washed free of soluble salt. We have thusprepared a barium silicate hydroxide.

msio's anon BaHSiO- OH Hi0 Silicic barium barium silicate water acidhydroxide hydroxide HaSiO:

Silicic barium barium silicate water acid hydroxide hydroxide 12,2oe,17a

Method B.-Compounds comprising the oxygenamphoteric metal radical andpolyvalent metals may be treated with strong bases inthe gaseous In thismethod, the alkali or wet condition. treatment is permitted to progressto a point just short of the break-down ofthe starting compound for wedo not Wish the treatment to result in disintegration. Examples of thematerials which we have prepared by this method are given by theseequations:

CaTiO; NHiOH HCa'liOzOEi NH; Calcium calcium titanate ammonia titsnatehydroxide BaTeOi I NaOH NaBa'IeOaOH Barium sodium barium tellurateteliurate hydroxide Method C'.A compound comprising theoxygen-amphoteric metal radical and an alkali metal may be heated orfused with an excess of an hydroxide of a polyvalent metal to yieldmaterials efiective for anion exchange according to our process.Exemplary reactions for the preparation of ferric arsenate hydroxide andbarium aluminate hydroxide are as follows:

KaASOi 3Fe(OH)a FezAsOdOH); SKOH 'Potassiuni ferric ierric arsenatepotassium arsenate hydroxide hydroxide hydroxide NaAlOg Ba(OH)zBaAlOAOH) NaOH Sodium barium barium aluininate sodium aluminatehydroxide hydroxide hydroxide Method D.Compounds containing exchangeablehydroxyl anions may be prepared from exchange compounds containing-otheranions'by treatment of these compounds with concentrated solutions ofhydroxides of various metals.

For example, a calcium metasilicate chloride,

CazSiOzCl, prepared by fusing an alkali metal silicate with calciumchloride, .may be treated with a strong solution of sodium hydroxide,'toyield a calcium metasilicate hydroxide, as follows:

QaiSi Ci9+2NaOH- Ca Si0 (OHh-l-ZNaCl Calcium sodium calcium sodiummetasilihydroxmetasllicate chloride eate ide hydroxide chloride Or wemay treat stannic aluminum nitrate with ammonium hydroxide, to obtainstannic aluminum hydroxide and ammonium nitrate as follows:

I Sn Al204(N0a):+2NH OH-i SnAlzO4(0H)z+2NH 4NOa stannicaluammonistannicaluamniominum um hyminum hynium nitrate droxide droxidenitrate In the examples of the preparation of the compounds as givenabove, the specific ratios which we have given are not controllingexcept that all the materials must be in excess over theoxygen-amphoteric metal radical compounds.

The materials which we have described may be used in the recovery ofvaluable anions and the removal of objectionable anions by the processof anion exchange. The manner of application of these materials ineffecting such a process is similar to the manner of application ofzeolites in the known processes of cation exchange. The liquidcontaining the anions which we wish to recover or remove is passed incontact with our new materials with the rate of fiow dependent.

upon the materials being used and the anions being exchanged. Variousmethods for carrying out the process will be apparent to thoseacquainted withthe water treatment art.

The following illustrative adaptations of the use of our process inefiecting anion exchange are given.

We may take one of the materials made in any of the methods describedabove, suchas barium silicate hydroxide for example, and pass throughthis materiala liquid containing anions which w'e'may wish to recover,for example, bromide ions. Upon analysis of the resulting eilluent, wefind that the bromide content has been materially reduced and is nowavailable for recovery in the exchange material. The exchange of. anionsis brought about in accordance with the following formula: i

Barium potasbarium otassium silicate slum silicate ydroxide hydroxidebrgbromide on e 'I'he fiow of the liquid being treated may be continueduntil tests indicate inefficient removal of the anions being exchanged,and the exchange material may then be regenerated with recovery of thedesired anion, as described below.

If it is desired to remove objectionable anions, such, for example, asthe fluoride ions from potable water, we may, for example, by usingstannic aluminate hydroxide as the exchange medium, effect a reaction inaccordance with the formula:

be desired to effect recovery. Bycontacting the liquid medium containingacid anions with any of the materials which are within the scope of ourinvention, we may efiect removal of the acids.

, As exemplary of the removal of phosphate ions through the use offerric arsenate hydroxide, we

show the following reaction:

remsoxoniwemirol reai soqrom-cNaon Fertic arsesodium ferric arsesodiumnate hydroxide phosnate phosphate hydroxphate ide vThe exchange materialwill then contain the phosphate ion while the liquid eflluent fromtreatment will contain sodium hydroxide.

Or if it is desired to remove the ion of cyanic acid through the use ofcuprictitanate hydroxide, an exchange of anions could be efiected inaccordance with the following equation:

Cu TiO;(OH);+2NaCN CUsTiOs(CN): +2NaOH Titanate sodium titanate sodiumhydroxide cyanide cyanide hydroxide Our new materials lend themselves tomany other adaptations in the new field of anion exchange.

When our exchange materials have become exhausted they may beregenerated by reversing the process of anion exchange. Those skilled inthe art will recognize the available methods of regeneration. However,we" describe one ofv the methods which we have found will completelyre-- generate our exhausted material. For example,

we may take the exhausted anion exchange ma- .liquid containing anionswith a compound conterial from the above described bromine removalprocess and treat this with a sodium hydroxide solution of moderateconcentration. The barium silicate bromide will thus be converted tobarium silicate hydroxide and the efiluent from the regeneration processwill contain sodium bromide in high concentration in accordance with thefollowing equation:

BaHSiOzBr-l-NBOH -o BaHSiO OH-i-NaBr Barium sodibarium sodisilicate umsilicate um bromide hy-' hydroxide brodirgxmide From the concentratedsodium bromide efliuent solution, the bromine may be recovered by any ofthe ordinary conventional methods.

There are innumerable applications of our novel process for effectinganion exchange. We have specifically indicated the recovery of acids andhalides as possible applications. Through the property of selectiveexchange by proper use and selection of material, we may effect removalof desired anions from liquids containing a number of ionizable salts.Our materials make possible the recovery of many types of acids fromwaste liquors, the recovery of which was impractical prior to thediscovery of these materials.

It is to be expressly understood that the foregoing description and theexamples we have given are merely illustrative and are not to beconsidered as limiting our invention beyond the scope of the subjoinedclaims.

We claim:

1. A process for effecting anion exchange in aqueous liquids 'whichcomprises reacting the taining within its molecule at least one -'-MAgroup and a radical composed of an amphoteric metal atom and at leasttwo oxygen atoms attached thereto, each MA group being linked by valenceto one of said oxygen atoms, and in steps of reacting the liquidcontaining anions with a compound containing within its molecule atleast one MA group and a radical composed of an amphoteric metal atomand at least two oxygen atoms attached thereto, each MA group beinglinked by valence to one of said oxygen atoms, and in which M representsa polyvalent metal and A represents an ionizable hydroxyl anion,regenerating the exchange compound by treating the same with an hydroxylanion containing. solution of moderate conoentration, and obtaining theanions from the effluent of the regeneration treatment.

3. A process for removal and recovery of halides from aqueous liquidswhich comprises the steps of reacting the liquid containing the halideswith a compound containing within its molecule at least one M'A groupand a radical composed of an amphoteric metal atom and at leasttwooxygen atoms attached thereto, each MA group being linked by valenceto oneof said oxygen atoms, and in which group M represents a polyvalentmetal and A represents an ionizablehy'droxyl anion, regenerating theexchange compound by treating the same with a hydroxyl anion containingsolution of moderate concentration, and obtaining the halides from theeilluent of the regeneration treatment.

4. A process for removal and recovery of acid anions from aqueousliquids which comprises the steps of'reacting the liquid containing theacid anions with a compound containing within its molecule at least oneMA group and a radical composed of an amphoteric metal atom and atleast'two oxygen atomsattached thereto, each 'M--A group being linked byvalence to one of said oxygen atoms, and in which group M represents apolyvalent metal and A represents an ionizable hydroxyl anion,regenerating the exchange compound by treating the same with a hydroxylanion containing solution of moderate concentration, and obtaining theacid anions from the'efiluent of the regeneration treatment.

OLIVER M. URBAIN. I WILLIAM R. STEMEN.

